1. Field of the Invention
This invention relates to a process for preparing a bicyclic .gamma.-lactone and, more particularly, it relates to an improvement in the process for preparing a bicyclic .gamma.-lactone represented by the formula (I) ##SPC3##
wherein R represents a hydrogen atom or a straight or branched chain alkyl group having 1 to 4 carbon atoms and n is an integer of 1 to 6.
2. Description of the Prior Art
The compounds of the formula (I) wherein n is 1 are well known to be useful as intermediates for the synthesis of prostaglandins as described in E. J. Corey and T. Ravindranathan, Tetrahedron Letters, 4753 (1971) and J. J. Partridge et al, Journal of the American Chemical Society, 95:21, 7171 (1973). Also, the compounds of the formula (I) wherein n is 2, 3 or 4 are useful since they constitute a partial structure of bicyclic .gamma.-lactones having physiological activities such as anti-cancer and antimicrobial activities which have recently been considered to be useful. The compounds of the formula (I) wherein n is 3 to 6 generally possess fragrance and are expected to be useful as perfumes or as intermediates for the synthesis of perfumes.
A typical conventional method for the synthesis of bicyclic lactones comprises condensing a cycloalkadiene with dichloroacetic acid chloride in the presence of triethylamine followed by a zinc treatment in acetic acid, and reacting the resulting product with hydrogen peroxide, as described in E. J. Lorey et al, Tetrahedron Letters, 311 (1970). However, this conventional method requires a number of steps and in addition requires an expensive starting material, dichloroacetic acid chloride and an expensive reagent, triethylamine, and therefore is not said to be an economical method. Further, the above conventional method has a disadvantage in that it produces a large amount of undesirable substances as by-products thereby decreasing the yield of the desired bicyclic lactones. Such formation of the by-products not only renders the method uneconomical but also requires additional steps for purifying the product.